Aftertreatment systems are often utilized to reduce emissions associated with operation of engines. The State of California and the United States Environmental Protection Agency have imposed stricter emissions requirements over time, adopting increasingly stringent standards for criteria pollutants, such as NOx, unburned hydrocarbons, carbon monoxide, sulfur dioxide, ozone, lead, and particulate matter. In addition to heat produced by engines themselves, aftertreatment systems incorporated in order to meet such requirements have contributed to excessive heat in the operation of such machines. Excessive heat associated with the engine or the aftertreatment systems may be further increased due to insulating structures designed to minimize noise transmitted to the surroundings, including the passenger compartment.
Various arrangements have been proposed for cooling the engine and related components. For example, U.S. Pat. No. 4,114,714 to Fachbach, et al. discloses a forced draft ventilation system that includes a first fan that pulls air through front grill and the radiator, and a second fan that receives air from an external inlet port directed forward the vehicle and forces the air across the engine, a portion of the heated air then being directed out of the engine compartment, and a portion of the heated air then being directed across the exhaust system and out of the vehicle. Inasmuch as the second fan is driven by the engine and is depicted as a relatively small device, and the inlet to the second fan is directed forward the vehicle, it would appear that second fan is dependent, at large in part, upon the forward movement of the vehicle to force fresh air to the second fan. Accordingly, the second fan may be unable to reduce adequately the engine compartment temperatures during idling situations, or when the machine travels in a direction such that the cab or other structure blocks ambient air flow into the engine compartment. Moreover, the air that is directed over the exhaust system has already been heated by moving over the engine itself, minimizing any resultant cooling of the exhaust components.
More recently, engine ventilation systems have been used to cool the enclosure or compartment that houses the engine and the aftertreatment systems. The engine ventilation systems may include one or more ventilation fans in addition to the engine radiator or air-to-air aftercooler fan. The engine compartment ventilation fan pressurizes the engine compartment and improves air flow through the compartment. Some machines, such as wheel loaders and hydraulic excavators, use hydraulic powered ventilation fans. Such fans are driven by a hydraulic motor having a shaft seal to prevent hydraulic fluid from leaking along the motor shaft. Should the motor shaft seal fail, hydraulic fluid may become entrained in the air flow stream exiting the ventilation fan and ultimately may be sprayed throughout the engine compartment. The operating temperatures of the aftertreatment components may be sufficiently high to ignite the hydraulic fluid, thereby presenting a potential fire hazard.